PROJECT SUMMARY: Understanding how variation in conserved genes and neural systems gives rise to variation in cognition and behavior is a fundamental goal of behavioral neuroscience. The unique genetic and behavioral features of Lake Malawi bower-building cichlids position them as a powerful species system for advancing this goal. Bower-building is a complex natural behavior in which males construct species-specific courtship structures in the sand. Bower-building behavior recruits conserved brain regions, such as the putative homologue of the mammalian hippocampus, that regulate social and spatial learning, memory, and behavior across species. Specific bower structures, such as crater-like ?pits? and mountain-like ?castles,? have repeatedly evolved in dozens of closely-related species. The unusually high degree of genetic similarity between species enables intercrossing of pit-digging and castle-building lineages in the laboratory, producing pit-castle hybrids. Remarkably, first generation (F1) pit-castle hybrids express both parental behaviors in sequence, first digging a pit and then building a castle. Phased expression of parental behaviors in F1 hybrids is associated with a unique pattern of gene regulation in the brain, whereby parental ?pit? alleles are upregulated during pit-digging, and parental ?castle? alleles are upregulated during castle-building (allele-specific expression; ASE). Such ?context- specific ASE? is a novel neurogenetic mechanism that may regulate neural and behavioral plasticity. The primary objectives of the proposed research are to (1) develop automated video and depth sensing systems to measure bower-building behavior for weeks at a time, (2) characterize several dimensions of bower-building behavior, (3) investigate the neural basis of species differences in bower-building behavior, and (4) investigate context-specific ASE in the brain during pit-digging and castle-building in F1 hybrids. The proposed research will integrate innovative technologies, next-generation sequencing approaches, and the strengths of a non- traditional species system to advance the field of behavioral neuroscience. More specifically, these experiments will generate fundamental knowledge about the neurogenetic basis of natural complex behavioral variation and a novel neurogenetic mechanism that may contribute to neural plasticity.